1. Field of the Invention
This invention relates generally to bearings for internal combustion engines and, more particularly, to main bearings including grooves for containing lubricating oil.
2. Description of the Prior Art
Main bearings support a rotating crankshaft of an internal combustion engine. Such bearings are subject to various loads, depending on the configuration of the engine, for example radial loads due to accessory belt tensions and thrust loads due to combustion pressures. As the crankshaft rotates, significant wear can develop along the inner surface of the main bearing. To reduce wear, internal combustion engines have been designed to include an oil pump supplying lubricating oil to the inner surface of the main bearing. Main bearings have also been designed to include an oil groove extending circumferentially along the inner surface to distribute the lubricating oil along the length of the inner surface. However, when the engine idles or stops, so does the oil pump, and the lubricating oil drains off the inner surface. Thus, the crankshaft is pressed against an inadequately lubricated inner surface, causing significant wear on the inner surface.
When the engine restarts, so does the oil pump, and lubricating oil is again supplied to the inner surface of the main bearing. However, there is a short delay before the lubricating oil is adequately distributed along the inner surface. Thus, for a short period of time, the crankshaft rotates on the inadequately lubricated inner surface, also causing wear on the inner surface. This delay is especially problematic in engines that stop and start frequently, such as engines of hybrid and electric vehicles, as the repeated starting and stopping incurs repeated delays, causing significant wear over time. In addition, crankshafts of hybrid and electric vehicles rotate at higher than normal speeds at startup, relative to crankshafts of conventional vehicles, creating a greater amount of wear on the main bearing.
In attempt to improve lubrication of the inner surface of the main bearing at engine startup, main bearings have been designed to include supplemental oil grooves, in addition to the circumferential oil groove. An example of such a main bearing is disclosed in U.S. Pat. No. 6,491,438 to Ono et. al. The main bearing disclosed in the Ono patent includes a plurality of branch oil grooves extending obliquely from a circumferential oil groove. When the engine is running, lubricating oil is pumped into the circumferential oil groove. The lubricating oil flows to the branch grooves and along the inner surface of the main bearing. When the engine idles or stops, the lubricating oil drains from the main bearing surface, but some of the lubricating oil is maintained in the branch oil grooves. When the engine restarts, the lubricating oil flows out of the branch oil grooves to the inner surface, according to rotation of the crankshaft. Thus, the inner surface of the main bearing is provided with some lubrication at startup, before a greater amount of lubricating oil from the oil pump reaches the inner surface.
However, in certain applications, the branch oil grooves of the Ono patent do not provide adequate lubrication between the crankshaft and the inner surface when the engine is idle or stopped, or at startup. In addition, the branch oil grooves of the Ono patent significantly reduce the non-grooved surface area of the main bearing, which reduces strength and load carrying capacity of the main bearing.